FIG. 7 depicts an operative relation between a well-known rocking member E and an over-centering coil spring C. As shown, the conventional rocking member E is journalled oscillatably on a base plate H through a shaft G. An end portion A of the coil spring C is engaged with an opening D formed in a front portion of the rocking member E. Another end portion B is engaged with an opening F formed in a base plate H. The base plate H has a pair of engagement pieces J and K, respectively formed in and placed at the symmetrical positions of a straight line I connecting the centers of the shaft G and the opening F, in order to restrict or control the range of movement of the rocking member E.
Due to such construction of the rocking member E and the base plate H, the rocking member E can be held at its one position whereat the member E abutting against the engagement piece J or its other position whereat the member E abutting against the other engagement piece K.
According to the conventional mechanism, after one leg or end portion A of the coil spring is made to be engaged with the opening D, the other end portion B of the coil spring C must be made to be engaged with the opening F, which is often small, with the coil spring C being compressed. It is apparent that such compressing operation of the coil spring is very difficult. The construction of the conventional setting-up apparatus for over-centering coil springs is explicitly simple, however if it is operated to set up the coil spring by a non-professional person, the coil spring C will be sprung off easily in a moment. It is more difficult when the coil spring C is to be set up in a complicated mechanism apparatus.